Rails in both railroad and light rail (typically, inner-metropolitan transport for persons) applications are subject to wear by the passage of trains over the rails. In particular, depressions in the upper surface of a rail may develop such that the railhead presents an undulating, corrugated surface. Moreover, the rail may develop burrs or otherwise lose its symmetrical profile (the profile that is transverse to the rail longitudinal axis). Maintenance of a smooth running surface on the railhead of a rail for railroad and light rail applications is important for reasons of safety, riding comfort, noise suppression, reduced maintenance of the track and track bed, and protection of the track, track bed and rolling stock.
Grinding machines for maintaining the railhead of rails in smooth, properly shaped condition are known. Such grinding machines generally comprise a plurality of rotatable grinding modules carried on a grinding vehicle and pulled by a locomotive or the like, and disposed in close proximity to the railhead surface of the rail. The grinding modules include rotatable, abrasive grinding stones that can be lowered into a position where a portion of the grinding stone bears on the rail surface. The grinding stones then grind and restore the surface of the railhead to a smooth properly profiled configuration.
In the past, there have been two types of grinding, commonly referred to as Type I and Type II. Type I grinding is as depicted in the prior art figures, FIG. 1a and FIG. 1b. As depicted, a grinding stone 10 is positioned on the railhead surface 14 of the rail 12 The grinding stone 10 is preferably approximately ten inches in diameter having a layer of grinding material 16 formed circumferential to a backing plate or hub 18. The grinding stone rotates about axis 20 as indicated by Arrow A in FIG. 1a. The grinding stone 16 rotates in a plane that is substantially coplanar with a vertical plane passed through the longitudinal axis of the rail 12. Type I grinding provides for surface grinding of the railhead. The grinding is moved in a longitudinal direction with the rail by advancing the carrying locomotive along the rail 12. Over time, the circumferential grinding surface 17 of the stone "dresses" to the rail, taking the shape of the railhead profile as depicted in FIG. 1b.
Type II grinding is utilized to profile the railhead of the rail. Profiling of a rail is accomplished by tilting the grinding module, and in particular, tilting the grinding stone 10 relative to the railhead 14 of the rail 12. Type II grinding is depicted in the prior art FIGS. 2a-2c. As depicted in FIGS. 2a and 2b, the grinding stone 10 is tilted in a more generally horizontal disposition, as compared to the vertical disposition of Type I grinding. Rotation of the grinding stone 10 is about axis 20 as indicated by Arrows B in FIGS. 2a and 2b. In Type II grinding, the grinding is performed such that the inner diameter 26 of the abrasive layer 16 is located generally over the railhead 14. Such grinding generates two potential contact areas 22, 24 in which the abrasive layer 16 may be in contact with the railhead 14 of the rail 12. At the contact areas 22, 24, the abrasive of the abrasive layer 16 is moving in a generally transverse direction to the longitudinal axis of the rail 12. Thus, the grinding surface of the abrasive layer 16 remains a flat surface and grinds a flat facet on the curved railhead surface 14.
In practice, as depicted in FIG. 2c, the profile of the railhead surface 14 of the rail 12 is re-profiled by a plurality of grinding stones 10 each set at a different angle with respect to the railhead 14 and each grinding a relatively small facet of the profile of the railhead 14. In some prior art devices, as many as one hundred grinding stones are utilized to re-profile the railhead 14 of the rail 12.
Examples of Type II rail grinding machines having tiltable grinding modules include U.S. Pat. No. 4,622,781 to Vieau et al. (assigned to the assignee of the present invention), U.S. Pat. No. 4,178,724 to Bruno, U.S. Pat. No, 3,707,808 to Danko et al., U.S. Pat. No. 3,606,705 to Rivorire, U.S. Pat. No. 2,197,729 to Miller, and U.S. Pat. No. 2,132,470 to Hobson et al.
A problem with Type I grinding is that it necessarily must be performed at relatively low revolutionary speed of the grinding stone 16. When using a relatively large diameter stone, such speed is typically in the range of 600-650 rpm. The Type I grinding results in longitudinal grooves being formed in the railhead surface 14. Further, due to slight imbalance of the grinding stone 16, chatter marks having a relatively long wavelength are frequently defined in the railhead surface 14. Such chatter marks are undesirable because they increase the noise of a vehicle riding on the rails 12 and increase noise and vibration in a rail car that is supported on wheels as the wheels pass over the chatter marks. The wavelength of the chatter marks is directly related to the rotational speed of the grinding stone 16 and the rate of advance of a grinding vehicle that carries the grinding module, a relatively slow rotational speed in combination with relatively slow speed of advance generating relatively long wavelength chatter marks.
Type II grinding is normally done at a much higher revolving speed, typically in the range of 3,000-3,600 rpm. Such high rotational speed results in chatter marks being defined on the surface of the railhead that have a much shorter wavelength than is normally experienced with Type I grinding. The short wavelength of the Type II grinding chatter results in such chatter being relatively imperceptible from an increased noise and increased vibration standpoint. A problem that occurs with Type II grinding, however, is the fact that when such grinding is complete, the profile of the surface of the railhead is defined by a plurality of facets. It would be preferable if the surface 14 of the railhead was formed of a continuous smooth profile.
An additional problem arises with respect to re-profiling LR or tram rail. As indicated above, LR refers specifically to transit systems typically installed in large metropolitan areas primarily for the transportation of persons. LR rail is depicted in the prior art Figure, FIG. 3. LR rail 30 has a profiled railhead surface 32. Unlike the railroad rail 12, depicted in FIGS. 1 and 2, LR rail 30 has an upward directed flange 34 on the gage (inner) side of the LR rail 30. The flange 34 has an upper surface that is generally coplanar with the surface of the railhead surface 32.
A difficulty with profiling LR rail 30 using the Type II grinding as described above, arises when attempting to profile the gage shoulder 36 and the field shoulder 38. When a grinding stone 10 is disposed at a large included angle with respect to the LR rail 30 in order to profile the gage shoulder 36, the outer circumference of the grinding wheel 10 comes into contact with the flange 34. Additionally, LR rail 30 is typically laid in paved areas, having pavement 40 disposed along side the LR rail 30. The pavement 40 is used to present a generally uninterrupted horizontal surface to facilitate pedestrian traffic and automobile traffic over the LR rail 30. When a grinding stone is disposed at a high included angle with respect to LR rail 30 in order to profile the field shoulder 38, the outer circumference of the grinding stone 10 bears upon the guard 40. Accordingly, there is a need to be able to profile the railhead 32 of LR rail 30 without also grinding on the flange 34 or the pavement 40.